The present invention relates to four wheel drive vehicles and more particularly to torque distribution on four wheel drive vehicles.
Conventionally, four wheel drive systems where manually switched between two wheel drive and four wheel drive. Recent advances have allowed for the drivetrain of the vehicle itself to operate in two wheel drive mode and recognize when the vehicle requires four wheel drive mode to drive optimally.
For a typical automatic four wheel drive vehicle system, the engine delivers torque to the transmission, which in turn transfers the torque to the transfer case. The transfer case divides the torque between the primary axle and the secondary axle based upon an input from a 4xc3x974 control module. During normal operation, the transfer case transfers torque only to the primary axle, and only divides the torque between the two axles on-demand that is, when the 4xc3x974 control module determines a need to transfer some of the torque to the secondary axle. The 4xc3x974 control module, in general, receives input from sensors that measure the speed of the primary axle relative to the secondary axle, among others, and employs these inputs to determine how much of the torque the transfer case should send to the secondary axle.
While this type of system is adequate for many driving conditions, it does not take into account whether the vehicle is towing a trailer or not. Under certain operating conditions while a vehicle is towing a trailer, it is advantageous to transfer additional torque to the secondary axle in order to reduce the overall load on the primary axle.
Thus, it is desirable to have an automatic four wheel drive system that can automatically adjust the torque distribution in order to operate optimally whether the vehicle is towing a trailer or not.
In its embodiments, the present invention contemplates a vehicle capable of adjusting a four wheel drive system when towing a trailer. The vehicle has an engine, a transmission operatively engaging the engine, and a transfer case, operatively engaging the transmission for receiving torque input therefrom, and having a primary torque output and a secondary torque output, and a clutch for selectively splitting the torque input from the transmission between the primary torque output and the secondary torque output. The vehicle also has a primary driveline operatively engaging the primary torque output, and a secondary driveline operatively engaging the secondary torque output. A trailer detector includes means for detecting the four wheel drive system is in a mode which allows for torque adjustment between the primary driveline and the secondary driveline; means for detecting an amount of torque demand; means for detecting the rotational velocity of a component of the primary driveline; means for detecting the rotational velocity of a component of the secondary driveline; means for conducting a plurality of tests to determine if preselected parameters exceed corresponding predetermined thresholds, employing the torque demand, the rotational velocity of the component of the primary driveline and the rotational velocity of the component of the secondary driveline; means for repeating the tests over a predetermined time interval; and means for detecting a trailer tow event if the parameters each exceed the corresponding predetermined threshold over the predetermined time interval.
The present invention further contemplates a vehicle trailer tow method employed with a vehicle having a four wheel drive system with a primary and a secondary driveline, the method comprising the steps of: detecting the four wheel drive system is in a mode which allows for torque adjustment between the primary driveline and the secondary driveline; detecting an amount of torque demand; detecting the rotational velocity of a component of the primary driveline; detecting the rotational velocity of a component of the secondary driveline; conducting a plurality of tests to determine if preselected parameters exceed corresponding predetermined thresholds, employing the torque demand, the rotational velocity of the component of the primary driveline and the rotational velocity of the component of the secondary driveline; repeating the tests over a predetermined time interval; and detecting a trailer tow event if the parameters each exceed the corresponding predetermined threshold over the predetermined time interval.
An advantage of the present invention is that a vehicle with an automatic four wheel drive system can automatically detect when it is towing a trailer and adjust the torque distribution between the axles accordingly. This automatic adjustment allows the secondary axle to assist the primary axle during high torque load events, thus allowing the primary driveline to avoid sustaining one hundred percent of the torque during high load trailer tow events.
Another advantage of the present invention is that by allowing for automatic adjustment of the torque distribution between the primary axle and the secondary axle during trailer towing events, a lower maximum torque specification is required for towing a particular weight of trailer, thus allowing for the use of a lower cost and weight primary axle.
A further advantage of the present invention is that the transmission shift points can be adjusted when a trailer tow situation is detected. Further, the fuel rates for the engine can be adjusted when a trailer tow situation is detected.